Department of Earth Science and Astronomy, The University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan.
Proc Jpn Acad Ser B Phys Biol Sci. 2006 Mar;82(1):25-32. doi: 10.2183/pjab.82.25.
Unique new fossil assemblages containing the large bivalve family Alatoconchidae are recorded from the Guadalupian (Middle Permian) shallow marine limestone in Kamura, Kyushu. The large bivalves occur in the Neoschwagerina Zone and Lepidolina Zone. This discovery establishes that the biostratigraphic range of the family Alatoconchidae extends up to the top of the Lepidolina Zone (upper Capitanian of upper Guadalupian) i.e., to the end-Guadalupian extinction level. The largest Alatoconchidae in Kamura occurs in the Neoschwagerina Zone, the size of which is up to 50 cm long and 5 cm thick. Although details are still unknown, their morphology with a wing-like side projection of their valves appears very similar to that of Alatoconchidae that includes the well-known genus Shikamaia Ozaki. The bivalve-bearing Iwato Formation was derived from a mid-oceanic shallow marine carbonate build-up formed on a mid-oceanic paleo-seamount. The close association among the Alatoconchidae, typical Tethyan fusulines (Verbeekinidae) and rugose corals (Waagenophyllidae), plus their common extinction pattern suggests that the Alatoconchidae flourished in warm, shallow (photic) marine environments in low latitude areas in Panthalassa as well as Tethys. The extra-large size and double-layered shell with a translucent outer layer composed of prismatic calcite suggests that these bivalves may have hosted abundant photosynthetic algal symbionts to support their large-body metabolism.
在日本九州的熊谷，古生代二叠纪瓜德鲁普世浅海灰岩中发现了含有大型双壳类阿拉孔贝科（Alatoconchidae）的独特新化石组合。这些大型双壳类化石出现在 Neoschwagerina 带和 Lepidolina 带。这一发现表明，阿拉孔贝科的生物地层范围一直延伸到 Lepidolina 带的顶部（上瓜德鲁普统的上卡匹坦阶），即瓜德鲁普纪末期灭绝水平。在熊谷，最大的阿拉孔贝科出现在 Neoschwagerina 带，其大小可达 50 厘米长，5 厘米厚。尽管细节尚不清楚，但它们的形态具有瓣膜的翼状侧突，与包括著名属 Shikamaia Ozaki 在内的阿拉孔贝科非常相似。产双壳类的岩田组源于大洋中浅海碳酸盐的堆积，形成于大洋古海山之上。阿拉孔贝科与典型的特提斯四射珊瑚（Verbeekinidae）和皱壁珊瑚（Waagenophyllidae）密切相关，它们共同的灭绝模式表明，阿拉孔贝科在潘塔西亚和特提斯洋的温暖、浅海（透光）环境中繁盛。特大尺寸和双层壳，外层由棱柱形方解石组成，具有半透明性，表明这些双壳类可能拥有丰富的光合作用藻类共生体来支持其大型代谢。
